1. Field of the Disclosure
The present disclosure relates generally to a system for generating power using a geothermal heat source and to a method of making geothermal power using the system.
2. Description of the Related Art
Some geothermal reservoirs have relatively high concentrations of non-condensable gases (NCG), such as carbon dioxide. NCG are generally considered undesirable because they increase cost and reduce efficiency of geothermal power plants.
Geothermal power plants generally employ condensers for condensing steam flow exhausted from turbines. The turbines are coupled to power generators used for producing electrical power. It is well known that, in general, lower condenser operating pressures result in more efficient power generation. However, the presence of relatively high concentrations of non-condensable gases in the steam can make it difficult to achieve desired low operating pressures, thereby decreasing efficiency. In addition, high concentrations of NCG mean that larger condensers and higher capacity vacuum equipment can be required to handle and remove the non-condensable gases, which results in increased capital costs for building geothermal power plants.
For steam turbine type geothermal power plants, there are essentially two main approaches for handling NCG, in addition to other approaches that are variations of these two approaches. A common approach, hereinafter referred to as the “standard” method, is to have a backend removal system that uses a compression system to remove the non-condensable gases from the vacuum condenser and compress them to slightly over atmospheric pressure prior to venting or treatment. This back-end NCG system typically consists of steam jet ejectors and/or vacuum pumps or turbocompressors. This is a good solution for reservoirs with low NCG content. However, for relatively high NCG content geothermal sources, this approach uses a large amount of steam for the jets or steam driven turbocompressor. In addition, the vacuum pumps and/or electric turbocompressors use large amounts of power.
The second method uses a “reboiler” device upstream of the steam turbine, which condenses the steam on one side of an exchanger and reboils it on the other side at a lower pressure. This creates a temperature driving force that powers the equipment. The non-condensable gases are vented from the upstream side of the reboiler and the lower pressure steam is sent to the turbine. Theoretically, this type of approach should work well. It has been tried experimentally, but there has been conflicting data as to how well it works in large scale geothermal power plants. Issues with this design may potentially include the loss of high pressure steam from the vent and the loss of steam pressure across the reboiler.
Other related methods and systems that are well known in the art are disclosed in an NREL report entitled “Comparative Analysis of Alternative Means of Removing Noncondensable Gases from Flashed-Steam Geothermal Power Plants,” Report No. NREL/SR-550-28329 (June 2000), available online at nrel.gov/analysis/tech—geo_analysis.html.
The present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the issues set forth above.